Stressed skin panel construction



June 10, 1969 R. HELLER 3,448,551

STRESSED SKIN PANEL CONSTRUCTION Filed Nov. 13, 1967 Sheet of 2 June 10,1969 R. HELLER STRESSED sxm PANEL consmucwron Filed Nov. 13.: 1967United States Patent US. Cl. 52222 14 Claims ABSTRACT OF THE DISCLOSUREA panel includes two sheet-material members arranged in spaced parallelplanes. A prestressed frame connects the two members locatedintermediate the same and is operative to permit limited movement of themembers with reference to one another and in the respective plane of themembers, to thereby compensate for different thermal expansion orcontraction of the two members.

Background of the invention The present invention relates to panels ingeneral, and more particularly to panels for structural andarchitectural purposes. Still more specifically, the present inventionrelates to panels which are particularly suitable for covering the outersides of exterior buliding walls and similar structures.

In modern architecture the use of such panels is becoming increasinglycommon, not only for aesthetic reasons, but also to afford good thermalinsulation at minimum possible specific weight. Of course, such panelsare expected to carry a certain amount of load and also to have maximumpossible shape-retaining ability.

The panels which are known for this purpose from the prior art includecompound panels whose major surfaces are covered with sheets of metal orlayers of other strong and inextensible material. However, theseconstructions are possessed of a major disadvantage, namely the factthat their inner and outer sides are subjected to highly significanttemperature differentials, for instance as a result of strong sunlighton the outer sides and/or of high external temperature, or of extremelylow external temperature with the inner side being subjected to heatingby heat emanating from the building. Such temperature differencesbetween the inner and outer sides of these panels may reach 50 C. andmore and of course strong heating or cooling will result in thermalexpansion or contraction of the sheet material member in question.Evidently, this will result in deformation of the panels and, ifadjoining panels are rigidly connected with one another or with a frame,undesired pressures and/or tensile forces develop. If the panels aresecured only locally the deformations are not checked at all and theexposed sides of the panels, that is the sheet material members, becomewavy as a result of these developing forces and will present anaesthetically displeasing appearance.

Summary of the invention The present invention provides a panel which isnot subject to the aforementioned disadvantages.

More particularly, the present invention provides a .panel whereindifferential heating and/ or cooling of the sheet-material membersforming the major surfaces of the panel will result only in dimensionalchanges in the respective members as a result of thermal expansion orcontraction, but will not cause other deformations of the re spectivemembers.

In accordance with one feature of my invention I provide, in a panel ofthe type here under discussion, a pair of sheet-material membersarranged in spaced parallel 3,448,551 Patented June 10, 1969 planes andbeing subject to differential changes of dimension in the respectiveplanes upon exposure to differential thermal conditions, and meansconnecting the sheet-material members and tensioning the same in theirrespective planes, the means being operative to effect independ-' entcompensation for dimensional changes of either of said members in therespective plane thereof to thereby maintain both of said memberstensioned irrespective of the dimensional changes.

The panel according to the present invention may, for instance, utilizea prestressed frame which, in accordance with one aspect of myinvention, may consist of a plurality of U-profiled members locatedintermediate the spaced parallel sheet-material members connected to thesame and supported on the prestressed members of an inner frame in sucha manner that they are tiltable about a central plane of symmetryextending intermediate and in parallelism with the planes in which thesheet-material members are located.

Other embodiments will be discussed subsequently, but regardless of theembodiment used, I have found it advantageous if one or more layers oflight weight thermally insulating material are disposed intermediate therespective sheet-material members, but are not bonded thereto insurfa'ce-to-surface contact to avoid influencing the prestressing whichhas been applied to the sheet-material members, Such insulating materialwill advantageously consist of inflammable inorganic material, such asrock wool, glass wool, or other material which may be admixed with abinder if desired. Various different materials may be used as thesheet-material members and I have found it very advantageous to utilizesurface improved metal foils consisting of aluminum alloys and having athickness of substantially 0.4 to 0.6 mm., or else of non-rusting steel.The use of such materials for the sheet-material members provides ahighly aesthetic appearance on structures equipped with my novel panels,and the attractive appearance thus provided will remain unchanged andwill not be influenced by changes in weather and/or temperatureconditions because of the constant tensioning of the sheet-materialmembers which is assured in accordance with my present invention.

In case of fire in a structure equipped with my novel panels it couldordinarily be expected that the shape-retaining ability or formstability of the novel panels, together with their load-supportingability and the connection to a concrete or steel wall skeleton would beweakened, particularly in cases where readily meltable aluminum foilsare used as sheet-material members. To guard against these problems Ihave found it advantageous to construct the frame members and theconnecting members of material which is more highly heat-resistant thanaluminum, for instance steel, and to secure eventually insertedfire-retarding layers by means of wire netting or of sheet metalconstructions which similarly consist of highly heatresistant materialsand which secure the fire-retarding layers to the frame members.

The novel features which are considered as characteristic-for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together wih additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawings.

Briew description of the drawing FIG. 1 illustrates a somewhat schematicsection taken on the line II of FIG. 2;

FIG. 2 is a somewhat schematic plan view of the em bodiment illustratedin FIG. 1;

FIG. 3 is a detail view of FIG. 1 on a considerably enlarged scale;

FIG. 4 is a view similar to FIG. 2, but illustrating another embodimentof the invention;

FIG. 5 is also similar to FIGS. 2 and 4, but illustrates yet anadditional embodiment of the invention;

FIG. 6 is a view similar to FIG. 1 illustrating another embodiment ofthe invention;

FIG. 7 is a detail view similar to FIG. 3 but illustrating yet a furtherembodiment of the invention; and

FIG. 8 is a transverse section through an additional embodiment of theinvention, shown in fragmentary form.

Description of the preferred embodiments Discussing now the drawing indetail, and firstly FIGS. 13 thereof, it will be seen that I haveillustrated there a panel structure which, as pointed out earlier, isparticularly suitable for covering exposed sides of wall structures inbuildings and the like, but which has general application for theconstruction of panel members. FIG. 2 shows most clearly that I providean inner supporting frame consisting of four individual members 1 ofsteel or similarly elastically shape-retaining and heat-resistantmaterial. The members 1 are connected to one another at their respectivejoints by double screws 2 which are inclined at a 45 angle and which arewell known in the art. Actuation of the screws 2 will push the adjoiningmembers 1 away from each other. FIG. 1 shows clearly that the outwardlydirected sides of the members '1 are rounded, and FIG. 2 shows in dottedlines that each of the members 1 is initially of arcuate outline.

A plurality of members 3, each of U-profiled crosssection, constitutetogether an outer frame. Each of the members 3 is supported with itsbase or bottom wall portion on the curved side of an associated one ofthe members 1 so as to be tiltable about the respective member 1 in thedirection indicated by the double-headed arrow shown in FIG. 1, namelyabout a central plane of symmetry located between and in parallelismwith the respective major surfaces of the panel.

To assemble the panel illustrated in FIGS. 1-3 the members 3 arearranged within an outer assembly frame (not illustrated). The members 1are arranged inwardly of the members 3 and, when the screws 2 areoperated, the members 1 are elastically deflected out of the initialpositions which are illustrated in FIG. 2 with dashed lines until theyassume the full-line positions illustrated in the same figure. Ofcourse, as this takes place they are pressed against the members 3 whichlatter are prevented from yielding to such pressure by the assemblyframe which is outwardly adjacent to them. Thus, the dual frameconsisting of the members 1 and 3 is placed into a prestressedcondition.

Once this is accomplished the sheet material members 4 are secured onopposite sides of the dual frame. These members 4 may consist of metal,for instance of surface improved aluminum sheets or non-rusting steelsheets having a thickness of 0.5 mm., for example, and securing of themembers 4 t0 the arms of the U-profiled members 3 is effected by bendingthe edge portions of the members 4 over the edges of the arms, asevident in FIGS. 1 and 3, this connection to be improved if necessary ordesired by spot welding or, bonding. The main point to remember is thatthe members 4 must be as taut as possible so as to be stretched in theirrespective planes. Upon removal of the thus completed panel from theassembly frame the outwardly directed tensioning forces generated by themembers 1 are equally distributed via the tiltably arranged U-profiledmembers 3 to the sheet-material members 4. It will be clear that iftemperature differentials develop between the two sheet material members4 of a panel constructed in accordance with my invention, that is if,for example, one of the members 4 expands more strongly than the other,wrinkling of the more strongly expanding member 4 is impossible and themember 4 thus expanding will remain tautly stretched because thedeveloping slack will be taken up by the outwardly acting stressesgenerated by the prestressed members 1 which act to outwardly deflectthe U-profiled members 3 to the extent to which this has been madepossible by the expansion of the sheet-material member 4 in question. Ofcourse, it being assumed that only one of the sheet-material members 4has expanded to this extent whereas the other has expanded less or notat all, the U-profiled members 3 will tilt slightly about the supportingmembers 1 in the direction towards the non-expanded or less stronglyexpanded sheet-material member 4. It will be clear that, if the conversetakes place so that one of the sheet-material members 4 is cooled to agreater degree than the other, and is therefore subjected to thermalcontraction greater than that which takes place in the other of thesheet material members 4, the increased stretching of the more stronglycooled sheet-material member 4 will be transmitted to other member 4 bytilting of the U-profiled members 3.

FIG. 3 illustrates that for static reasons it is advantageous to havethe bottom wall of the members 3 configurated as a tubular profile,advantageously of quadratic or rectangular cross-section. It is alsoshown in FIG. 3 that insulating tapes or strips 5 of synthetic plasticmaterial are arranged between the arms of the members 3 and thebent-over edge portions of the sheet-material members 4 to eliminatethermal bridging at these points and to also reduce the development andtransmission of noise.

FIGS. 6 and 7 show constructions which essentially are the same as thatshown in FIGS. 1-3. The difference in FIG. 6 is the use of a thermallyinsulating layer or plate 6 which is disposed intermediate the sheetmaterial members 4. A similar layer 6' is shown in FIG. 7. In both casesthe layers 6 or 6 are advantageously constructed of non-flammablematerial which should have at least a certain stability, and for thispurpose I have found rock wool or expanded mica which is compressed intoplateshape with sodium silicate, to be advantageous although othermaterials are of course usable. FIG. 7 differs from FIG. 6 in the mannerin which FIG. 3 differs from FIG. 1, namely in the construction of themembers 3 and in the provision of the members 5, and further in that thelayer 6 is supported by wire mesh 7, or similar heatresistant supportingmembers, which are secured to the members 3 and which are intended toinsure that the novel panel has sufficient stability to prevent collapseeven if the sheet-material members 4 should be destroyed, for instancein case of a fire.

Coming now to the embodiment illustrated in FIG. 4 it will be seen thatthis differs from FIGS. 1-3 in the arrangement employed for prestressingof the frame. In FIG. 4 there are provided adjusting organs 8 locatedwithin the confines of the members 1 outwardly adjacent of which themembers 3 are arranged. Each of the adjusting organs 8 comprises atubular member and a pair of screws 80' threaded into the opposite openends of the tube 80. There is further provided a member 9 having theconfiguration of a cross and comprising four tubular portions each ofwhich has arranged therein a spring 90b. Received in each of theextensions 90a is a supporting arm or rod 900 which is urged outwardlyin the direction of the arrows associated with the respective arms 900.It is clear from a construction of FIG. 4 that the screws 80" serve topull the opposite ends of the members 1 inwardly and to elasticallydeform them against the action of the arms 90c. If, upon aflixing of thesheetmaterial members 4, the screws 80' are again relieved, the nowprestressed members 1 will serve to maintain the members 4 in thedesired stretched condition in the manner in which this has beenoutlined earlier.

A further embodiment in accordance with the present invention isillustrated in FIG. 5 in somewhat schematic form. It will be seen thatthe sheet material members 4 have again been identified with the samereference numeral as previously, whereas the U-profiled members 3 havebeen omitted for the sake of clarity. In place of the members 1, theembodiment of FIG. 5 employs an inner frame which consists of twoarcuately curved end pieces 11 and two arcuately but inwardly curvedside pieces 12. A screw-type pressure-applying arrangement of well-knownconstruction is arranged intermediate the side pieces 12 and, whenoperated, exerts thereupon pressure in the direction of the dual arrowsassociated with the arrangement 10, thus prestressing the members 12 andthereby the members 11 and providing the desired prestressing which hasbeen discussed with reference to FIGS. 1-3 earlier.

Coming, finally, to the embodiment illustrated in FIG. 8, it will beseen that this illustrates yet a further approach in accordance with myinvention. In FIG. 8 the sheet-material members are identified withreference numerals 24. They are arranged, as in all other embodiments,in two spaced parallel planes. Located intermediate these planes in acentral plane of symmetry which is in parallelism therewith is an innerframe which is stiffened by the members 21 which are parallel bars.Members 23 having a U-shaped profile and consisting of spring steel aresupported on the frame 20 in such a manner that their arms extend inoutward direction. In their non-tensioned state the members 23 have theconfiguration illustrated in dot-dash lines in FIG. 8, it being notedthat they are provided with a central longitudinal depression in whichthe edge of the frame 20 is received as clearly visible in FIG. 8. Toeffect assembly of the embodiment illustrated in this figure the members23 are deflected from the dot-dash line position into the fulllineposition, whereupon the sheet-material members 24 are secured to them bybending the edge portions of the members 24 over the arms of the members23 and/or otherwise effecting a connection, for instance by means ofspot welding, bonding or the like. In any case, the permanent tendencyof the members 23 to return from their full-line position into theirnormal position in which they are relaxed and have the configurationshown in dotdash lines, will permanently stretch the members 24 and keepthem taut. Of course, the members 23 are tiltable about the edge of theframe 20 received in the groove in these members 23, and this is for thepurposes which have been outlined earlier. Arranged intermediate thesheet-material members 24 are two layers or plates 26, one disposed oneach side of the frame 20, consisting of thermally insulating materialand/or non-flammable or fire retarding material. These layers 26 areadvantageously secured to the members 21 of the frame 20.

The advantages of the present construction will have become obviousalready. It will therefore suffice to merely point out once more thatthe panel in accordance with the present invention is of light weightwhile exhibiting great form stability and load-carrying ability. Suchpanels are very well suited for covering the exposed sides of buildingwalls, whether solid or skeleton wall constructions, and the fact thatthey have very good thermally insulating properties make themparticularly suitable for such applications. Inasmuch as a large varietyof different materials can be used for the sheet-material members whichconstitute the major surfaces of the panels makes it possible to selectthe sheet-material according to the specific requirements of asituation, for instance by using surface treated chrome-nickel steel orthe like, and it is clear that this makes it possible to provide abuilding covered with my novel panel with an aesthetically pleasingappearance which will always remain attractive and unchanged, regardlessof changing weather and/or temperature conditions.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofstructures differing from the types described above.

While the invention has been illustrated and described as embodied in apanel structure, it is not intended to be limited to the details shown,since various modifications and structural changes may be made withoutdeparting in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims.

1. A panel, particularly for covering the exposed sides of a wallconstruction on buildings and the like, comprising a pair ofsheet-material members arranged in spaced parallel planes and beingsubject to differential changes of dimension in the respective planesupon exposure to differential thermal conditions; and means connectingsaid sheet-material members and tensioning the same in their respectiveplanes, said means including pretensioned frame means interposed betweensaid members and comprising an outer frame having a first pair of spacedparallel frame portions and a second pair of spaced parallel frameportions loosely extending intermediate said first frame portions, and apretensioned inner frame located within the confines of said outer frameengaging said frame portions and urging the same outwardly away from oneanother, said members being connected to said frame portions and beingtensioned by being operative to effect independent compensation fordimensional changes of either of said members in the respective planethereof to thereby maintain both of said members tensioned irrespectiveof dimensional changes in either of said members individually or in bothof said members together.

2. A panel as defined in claim 1, wherein said frame portions are eachengaged and supported by said pretensioned frame for tilting movementtransversely of a central plane of symmetry of said panel which islocated between and parallel to said planes.

3. A panel as defined in claim 2, wherein said frame portions are ofprofiled cross-sectional configuration.

4. A panel as defined in claim 2, wherein said frame portions are ofsubstantially U-shaped cross-section and each have a bight and a pair ofarms, and wherein the bights of each pair of frame portions faceinwardly towards one another.

5. A panel as defined in claim 1; and further comprising at least onelayer of thermally insulating material interposed between said members.

6. A panel as defined in claim 5, wherein the material of said layer isnon-combustible.

7. A panel as defined in claim 6; and further comprising at least onereinforcing support element supporting said layer and connecting thesame to said frame means.

'8. A panel as defined in claim 7, wherein said support element consistsof a material having a resistance to heat greater than that of saidsheet-material members.

9. A panel as defined in claim 8, wherein said support element is awire-mesh element.

10. A panel as defined in claim 1; and further comprising at least onelayer of lightweight thermally insulating material interposed betweensaid members.

11. A panel as defined in claim 1, wherein said second pair of frameportions extends between but is separate from said first pair, saidframe portions each being of substantially U-shaped cross-section withthe bights of the portions of the respective pairs facing one another,said frame portions consisting of spring steel having a permanenttendency to flex outwardly about a line of symmetry extendinglongitudinally of the respective bight intremediate the respective arms,and said members being connected to said arms and maintaining said framerportions against such flexing, said means further comprising rigidsupport means extending between and engaging the bight of the frameportions of the respective pairs and being operative for maintainingsaid frame portions of the respective pairs in predetermined spacedrelationship with one another.

12. A panel as defined in claim 1, wherein said outer frame is ofoutwardly open substantially U-shaped crosssectional configuration andsaid frame portions are transversely spaced arm portions provided withoppositely directed side faces, said members each overlying one of saidside faces and having respective edge portions each connected to one ofsaid arm portions.

13. A panel as defined in claim 12; and further comprising elements ofelastomeric material interposed between the respective arm portions andmembers assoeiated therewith.

14. A panel as defined in claim 13, wherein said elastomeric material isa thermally insulating material.

References Cited UNITED STATES PATENTS 948,450 2/1910 Hussey 526201,708,351 4/1929 Auld 52222 1,910,608 5/1933 Junkers 52222 2,350,513 6/1944 Leadbetter 52-145 2,805,739 9/1957 Dennison 52-222 3,180,220 4/1965Jeffree 160-378 3,267,626 8/1966 Daly 52-619 F HENRY C. SUTHERLAND,Primary Examiner.

U.S. Cl. X.R.

